1. Field of the Invention
The field of the invention is that of home audiovisual networks of the type used to interconnect a plurality of audio and/or video analog and/or digital type terminals (also called devices) so that they exchange audiovisual signals.
These terminals belong, for example, to the following list of equipment (which is not exhaustive): television receivers (using satellite, RF channels, cable, xDSL and other means), television sets, video tape recorders, scanners, digital video cameras, digital cameras, DVD readers, computers, personal digital assistants (PDAs), printers, etc.
The home audiovisual networks are, for example, of the high-bit-rate switched type comprising a small number of nodes, used especially for the real-time exchange of moving pictures for distribution within a dwelling.
The home audiovisual networks according to the invention comprise a plurality of nodes connected by a plurality of physical communication links. These links are for example of the type used for two-way data transfers according to the IEEE 1355 standard.
Audio and/or video terminals communicate with one another through the nodes to which they are connected. The nodes that form the skeleton of the network comprise especially:                first interface means enabling the connection, through one or more links (for example according to the IEEE 1355 standard), of one or more other nodes;        second interface means used for the connection of one or more analog terminals (namely terminals capable of receiving audiovisual signals in analog form);        third interface means used for the connection (for example through a digital bus according to the IEEE 1394 standard) of one or more digital terminals (namely terminals capable of receiving audiovisual signals in digital form).        
A home audiovisual network of this kind works as follows: a connection is set up, through a plurality of nodes, between a first terminal (or listener) that seeks to receive audiovisual signals and a second terminal (or talker) that can give it these signals.
Some elements of the terminology used hereinafter in the description shall now be specified.
The first terminal mentioned here above, namely the listener, is called a “destination terminal” and the node to which it is connected is called a “destination node” or “display unit”.
In the case of the second terminal mentioned here above, two cases may be distinguished.
In a first case, this second terminal is integrated into a node called a “source node”. Thus, it is assumed that the source node comprises means for the reception and/or reading of source signals (originating outside the network) and means for the transmission of these source signals, in the form of the above-mentioned audiovisual signals, to the destination node. In other words, the source node receives and/or reads source signals and introduces them into the home audiovisual network in the form of audiovisual signals. In this first case, the (source) node and the second terminal are one and the same.
The present invention can be applied preferably to the case where the source node includes a television receiver (for example in France a “TPS” (registered mark) receiver or “Canal Satellite” (registered mark) receiver). In this case, the source node is also called a “Tuner Unit”. It enables the direct introduction into the network, in digital form (generally encoded in the MPEG2 format) of source signals given by an operator and containing television programs.
In a second case, the second terminal called an “input terminal” is connected to a node called an “input node”. Unlike the first case, the (input) node and the second terminal are not one and the same. The input node does not have means for the reception and/or reading of source signals (originating outside the network). The input node receives audiovisual signals coming from the input terminal and introduces them into the home audiovisual network.
The term “input terminal” is understood to mean for example a camcorder, a digital camera, a digital output DVD reader or any analog device seen through an analog/digital converter.
More specifically, the invention relates a system for the transmission of audiovisual signals comprising several home audiovisual networks as mentioned here above.
The invention has many applications such as, for example, a system for the transmission of audiovisual signals within a building, where each household possesses (at least) one home audiovisual network (which is a private network).
Such a system must enable the sharing of at least one source node (for example a “tuner unit”) by the plurality of home audiovisual networks while, at the same time, complying with the rights of access to the audiovisual signals transmitted by the source node. In other words, each destination or listener terminal should be capable, provided that the user has the necessary authorization, of receiving audiovisual signals transmitted by the source node (through the destination node to which it is connected). Typically, the authorization consists of a subscription by the user with an operator (for example a television provider).
Such a system must also enable exchanges of audiovisual signals between home audiovisual networks. In other words, each listener or destination terminal of a home audiovisual network should be capable of receiving audiovisual signals (through the destination node to which it is connected), audiovisual signals transmitted by an input node (which must not be mistaken for a source node as explained here above).
Here below in the description, the term “pay-contents” is used to describe the audiovisual signals transmitted by a source node (for example a “tuner unit”). Furthermore, the term “user-contents” is used to describe the audiovisual signals transmitted by an input node (which receives audiovisual signals coming from an input terminal, for example a digital camera).
To date, there is no known system having these characteristics (namely source nodes shared by a plurality of home audiovisual networks and exchanges of audiovisual signals between home audiovisual networks).
A system of this kind must also enable the control of the reproduction (copying) and/or the broadcasting of audiovisual signals introduced by the source node or nodes shared by the plurality of home audiovisual networks.
It will be understood, for example, that an operator who supplies source signals containing television programs to a source node would want some (or even all) these programs to be incapable of being copied (i.e. pirated) by a user of the network who has a terminal, in this network, fitted out with means for recording on a data medium.
2. Description of the Prior Art
In a first known mechanism for the protection of audiovisual signals when they are digital type signals, a DTCP format encoding is applied to these signals (see detailed explanation here below with reference to the figures). This first known protection mechanism assumes the presence of DTCP format encoding means at one end and corresponding decoding means at the other end. Now DTCP format encoding or decoding means are very costly at present. It is therefore not possible to consider equipping each node of the network with such means.
In a second known protection means, audiovisual signals, when they are analog type signals, are partially scrambled in order to prevent them from being copied. An anti-copy scrambling of this kind is done for example according to the “Macrovision” (registered mark) standard (see detailed explanation here below with reference to the figures). This second known protection mechanism cannot, at present, be implemented and activated systematically in all the destination nodes of the home audiovisual network to which analog terminals are connected. Indeed, the user should be left with the possibility of copying certain audiovisual signals which are not subjected to any special protection. For example, he is allowed to make a video tape recording of a program broadcast on a public television station.
It can be seen therefore that the two known protection mechanisms described here above (DCTP and “Macrovision”) cannot be used alone or in combination to provide optimum protection to audiovisual signals at an acceptable cost.